Subi Tharmalingam

Novel 5-HTTLPR Allele Associates with Higher Serotonin Transporter Binding in Putamen: A [11C] DASB Positron Emission Tomography Study

BACKGROUND The serotonin transporter (5-HTT)-linked polymorphic region (5-HTTLPR) has two frequent alleles, designated long (L), and short (S). The S allele is associated with lower levels of 5-HTT mRNA and lower 5-HTT expression in human cell lines. A functional single nucleotide variant was detected within L, designated L(A) and L(G). Only L(A) is associated with high levels of in vitro 5-HTT expression, whereas L(G) is low expressing and more similar to S. We examined the possible influence of the long (A/G) variant on 5-HTT density in the living human brain using 3-(11)C-amino-4-(2-dimethylaminomethylphenyl-sulfanyl) benzonitrile ([(11)C]DASB) positron emission tomography. METHODS The 5-HTT binding potential (5-HTT BP), an index of 5-HTT density, was found in 43 healthy subjects genotyped for 5-HTTLPR long (A/G), and in an ethnically homogenous subsample of 30 Caucasian-Canadians. RESULTS The L(A)/L(A) was associated with higher 5-HTT BP in putamen (p = .026, not corrected). This association became stronger in the Caucasian subsample (p = .004) and was significant even after correcting for multiple comparisons. CONCLUSIONS The 5-HTTLPR long (A/G) polymorphism influences 5-HTT density leading to higher putamen 5-HTT BP in healthy L(A)/L(A) carriers of Caucasian ancestry. This finding extends the role of this polymorphism from in vitro reports of higher 5-HTT expression with the L(A)/L(A) genotype into in vivo brains of healthy human subjects.

Association of the Val158Met Catechol O-Methyltransferase Genetic Polymorphism with Panic Disorder

Genetic as well as clinical data suggest that catechol O-methyltransferase (COMT) is involved in multiple complex psychiatric conditions. Recent studies have described an association between the Val158Met COMT polymorphism and panic disorder. Other recent investigations provide evidence that there are other loci within or nearby the COMT gene that may contribute to the susceptibility to panic disorder. To further evaluate the influence of the Val158Met COMT polymorphism in panic disorder we genotyped this marker in the coding region of the COMT gene and two additional variants (rs737865 and rs165599) in the 5′ and the 3′ region, respectively, in two independent Canadian samples: 121 nuclear families, and 89 cases with matched controls. In the nuclear families, significant transmission disequilibrium for the valine allele was observed between the alleles of the Val158Met COMT polymorphism and panic disorder (p<0.01). A significant excess of the valine allele was found in analysis of the case–control sample (p<0.01). This effect was mainly derived from the subgroup of females. This finding, including the female effect, replicates earlier results in studies of the Val158Met polymorphism in panic disorder. No significant results were found for the other two markers. These results support the hypothesis that the valine allele of the Val158Met COMT polymorphism or a nearby locus is involved in the etiopathogenesis of panic disorder.

The dopamine-4 receptor gene associated with binge eating and weight gain in women with seasonal affective disorder: an evolutionary perspective.

BACKGROUND We recently described a preliminary association between the hypofunctional seven-repeat allele of the dopamine-4 receptor gene (DRD4) and increased maximal lifetime body mass index in women with seasonal affective disorder (SAD). In this study, we examined whether binge eating behavior mediated this putative association. METHODS The study sample consisted of 131 women with winter SAD who reported increased intake of high-carbohydrate/high-fat foods during depressive episodes. We compared rates of binge eating behavior in the two genotypic groups defined by the presence or absence of the seven-repeat allele of DRD4. RESULTS Consistent with our working hypothesis, the proportion of binge eaters was significantly greater in probands with the seven-repeat allele (18 of 46, 39.1%) than in probands without this allele (14 of 85, 16.5%) [chi(2)(1)= 8.32, p = .004; odds ratio = 3.25, 95% confidence interval 1.43, 7.41]. CONCLUSIONS Pending replication in other samples, these results point to a genetic factor that could help in the early identification and treatment of women at higher risk for seasonal weight gain associated with binge eating behavior. At a theoretic level, the current results suggest a novel link between evolutionary models of seasonal weight gain on the one hand and the DRD4 gene on the other.

Childhood inattention and dysphoria and adult obesity associated with the dopamine D4 receptor gene in overeating women with seasonal affective disorder

There is significant evidence that altered dopamine activity plays a role in seasonal affective disorder (SAD). The current study examined three separate genetic hypotheses for SAD related to the 7-repeat allele (7R) of the dopamine-4 receptor gene (DRD4), a variant associated with decreased affinity for dopamine. We examined the possible contribution of 7R to the overall expression of SAD, attention deficit disorder (ADD) comorbidity, and body weight regulation. As part of an ongoing genetic study of increased eating behavior and mood in female subjects, 108 women with winter SAD and carbohydrate craving/weight gain were administered the Wender-Utah Rating Scale to measure childhood ADD symptomatology, and a questionnaire to assess maximal lifetime body mass index (BMI). To test for an association between 7R and the categorical diagnosis of SAD, the transmission disequilibrium test (TDT) was used in a subsample of probands providing familial DNA. Standard parametric tests were used to compare childhood ADD symptoms and maximal lifetime BMI across the two genotypic groups defined by the presence or absence of 7R. The TDT found no initial evidence for an association between 7R and the categorical diagnosis of SAD. However, 7R carriers reported significantly greater inattention and dysphoria in childhood (p=0.01 and 0.001, respectively) and a higher maximal lifetime BMI (p=0.007) than did probands without this allele. Furthermore, excluding probands with extreme obesity (maximal BMI >40), a strong correlation was found linking childhood inattentive symptoms and maximal lifetime BMI (r=0.35, p=0.001). In overeating women with SAD, the 7R allele of DRD4 may be associated with a unique developmental trajectory characterized by attentional deficits and dysphoria in childhood and mild to moderate obesity in adulthood. This developmental course may reflect different manifestations of the same underlying vulnerability related to central dopamine dysfunction. Given the possibility of population stratification when studying genotype/phenotype relationships, future use of genomic controls and replication of our findings in other overeating and/or ADD populations are needed to confirm these initial results.

Analysis of the novel TPH2 gene in bipolar disorder and suicidality

SIR—Genetic factors have been generally implicated in the etiology of suicide, although the precise mechanism and amount of the genetic contribution are not yet well established. The serotonergic system is thought to be trait dependent and associated with disturbances in the regulation of anxiety, impulsivity, and aggression. Furthermore, serotonergic dysfunction has been suggested in suicide based on several observations. For example, low concentration of the metabolite of serotonin (5-HIAA), in CSF has been associated with suicide attempts and completed suicide, and low levels of 5-HT or 5-HIAA were also observed in suicide victims. 5-HT is synthesized in two steps, with tryptophan hydroxylase (TPH) as the rate-limiting enzyme. Thus far, two TPH genes have been identified. The TPH1 gene is located on chromosome 11p15 and has been the focus of a number of genetic studies of suicidality. A recent meta-analysis concluded that the TPH1 intron 7 A218 polymorphism is associated with suicide-related behavior. Interestingly, a new TPH gene (TPH2) located on chromosome 12q21 has recently been described. In mice brain stem, expression of TPH1 appears to be 150 times lower than TPH2, suggesting that TPH2 may play a much more important role in serotonin synthesis in the brain than TPH1. Therefore, we were interested in investigating the putative role of the TPH2 gene in suicide attempters using a large and well-characterized sample of patients with bipolar disorder. TPH2 has three highly polymorphic single-nucleotide polymorphisms (SNPs): hCV245410 (C/T), hCV8376173 (A/G), rs1487280 (A/G). These SNPs are located in introns 1, 5, and 8, respectively. The study population consisted of 336 bipolar patients from 305 families who were recruited in the Toronto area. The mean age at the time of the interview was 35.36710.37 SD. Subjects ranged in age from 16 to 67 years (35710 SD). The mean age at onset for bipolar disorder was 2077.58 SD. Female subjects comprised 62% of the sample. A total of 86 patients attempted suicide. The SCID-I was administered to all subjects by trained clinical interviewers. Suicidality was assessed on a quantitative scale, with the following order: 11⁄4Thoughts of death, 21⁄4Suicide Ideation, 31⁄4Suicide Plan, 41⁄4Suicide Attempt. Among the bipolar patients, 267 patients had history of suicide ideas or attempt and the mean score for all 336 suicide ideation/behavior scores was 2.171.4. The genoptypes of TPH2 hCV245410, hCV8376173, and rs1487280 polymorphisms were determined by Taqman assay (ABI 7000). Allelic and haplotype transmission tests in suicide attempters were performed using TDT and TRANSMIT. The Family Based Association Test (FBAT) was used for analyses of suicide ideation/behavior quantitative traits. All the analyses were performed under the assumption of an additive model. Main results for single marker TDT in attempter patients are shown in Table 1. For the haplotypes of these three polymorphisms in the attempter population, the TRANSMIT analysis showed a nonsignificant global w (0.56, 5 df). When the suicide behavior was analyzed as a quantitative trait by FBAT, no significant differences were found for hCV245410 (z1⁄4 0.051 P1⁄40.959467), hCV8376173 (z1⁄40.090 P1⁄40.928282), and rs1487280 (z1⁄4 0.143; P1⁄40.886). All the eight possible haplotypes showed no significant results when weighted on the suicide behavior as the quantitative trait (Table 2). In bipolar patients, the TDT did not show significant bias for hCV245410 (109 vs 109 transmissions), hCV8376173 (106 vs 104), and rs1487280 (100 vs 105). The global w using TRANSMIT analyzing only frequent haplotypes was not significant in the overall sample (1.8874, 5 df). To our knowledge, this is the first association study between the TPH2 gene and bipolar disorder and suicide behavior. Our results indicate that it is unlikely that the hCV245410–hCV8376173–rs1487280 haplotypes are involved in the suicide behavior in our bipolar sample. The three variants chosen in this study are polymorphic enough to provide good statistical power for this family study design. Moreover, mutation screening of the TPH2 promoter could be very valuable and these 50 flanking variants might be involved in suicide behavior because of the prior evidence that the immunoreactivity and the expression of TPH in the brains of suicide patients is higher. Despite the fact that bipolar disorder has been shown to have a strong genetic component and the serotonergic system is implicated in the pathogenesis of the disorder, we found that all haplotypes of the TPH2 gene were without bias to bipolar probands in the total sample. Although possible biological differences between suicidal ideation and attempted suicide are pointed out in TPH1 association studies where the 218A/C polymorphism was associated with suicide attempt but not with suicide ideation, the main strength of this study is the family-based strategy that is not sensitive to population stratification, the large sample size, and the suicide quantitative trait Molecular Psychiatry (2004) 9, 896–899 & 2004 Nature Publishing Group All rights reserved 1359-4184/04

A birth-season/DRD4 gene interaction predicts weight gain and obesity in women with seasonal affective disorder: A seasonal thrifty phenotype hypothesis.

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Association of HPA axis genes with suicidal behaviour in schizophrenia

We have recently described an association between the hypofunctional 7-repeat allele (7R) of the dopamine-4 receptor gene (DRD4), weight gain, and obesity in women with seasonal affective disorder (SAD). In the current study, we examined whether season-of-birth might interact with the 7R allele to influence body weight regulation in SAD. In 182 female probands with SAD, we performed an analysis of covariance predicting maximum lifetime body mass index (BMI) with both the exon-3 variable number of tandem repeat polymorphism of DRD4 and season-of-birth as independent variables, and age as the covariate. The overall model was highly significant (F=4.42, df=8, 173, p<0.0001) with season-of-birth predicting maximal lifetime BMI both on its own and in its interaction with the 7R allele. The latter finding was attributable to 7-repeat carriers born in the spring (N=17), who had a mean maximal lifetime BMI of 33.7 kg/m2 (SD 8.6), compared to 26.7 kg/m2 (SD 5.4) for all other probands combined (N=165) (F=20.01, df=1, 179, p<0.0001). The lifetime rate of obesity (maximal BMI >30 kg/m2) was also significantly higher in the 7R/spring birth group (9/17=52.9% vs 32/165=19.4%; χ2=9.94, df=1, p=0.002; odds ratio=4.68, 95% CI=1.67–13.07). These data may reflect a novel gene–environment interaction, during early brain development, which establishes an increased risk for obesity in women with SAD. Although the mechanism for season-of-birth effects in psychiatric disorders is unknown, a characteristic pattern of melatonin exposure during the second and third trimesters may be of particular relevance in this study population. We speculate that these data may reflect the vestigial expression of a seasonal thrifty phenotype that contributed to the positive selection of the 7R allele over the past 40 000 years.

Association study between the novel functional polymorphism of the serotonin transporter gene and suicidal behaviour in schizophrenia

Family, adoption and twin studies show that genetics influences suicidal behaviour, but do not indicate specific susceptibility variants. Stress response is thought to be mediated by the corticotrophin-releasing hormone (CRH), which is known to be a regulator of the hypothalamic-pituitary-adrenal pathway (HPA). Alterations in HPA system have been related to impulsivity, aggression and suicidal behaviour, common feature in schizophrenia. CRH is the hypothalamic factor that stimulates the pituitary gland. To search for markers conferring genetic susceptibility to suicide, we typed six HPA axis genes (CRH, CRHR1, CRHR2, CRHBP, MC2R, NC3R1) in a cohort of 231 subjects with schizophrenia in which 81 attempted suicide. The genotype analyses yielded significant association between CRH binding protein (CRHBP) and suicide attempt (P = 0.035). The genotype analysis for quantitative measures of suicidal behaviour showed no association. The interaction analysis showed a significant interaction between CRH receptor type 1 (CRHR1) and CRH binding protein (CRHBP) in influencing suicide attempt and the severity of suicidal behaviour. Current results show that genetic variation in HPA axis genes could be associated with suicidal behaviour in schizophrenia. This is to our knowledge the first study on suicidal behaviour investigating the interaction among the HPA axis genes.

GENE-GENE INTERACTION BETWEEN MAOA AND COMT IN SUICIDAL BEHAVIOR

A serotonin transporter gene linked polymorphic region (5-HTTLPR) has been investigated in several genetic association studies, including studies of schizophrenia and suicidality. The current study was designed to examine whether the new long (A/G) variant polymorphism of the 5-HTT gene may be associated with suicide attempts of 290 Caucasian schizophrenic patients. Among these patients, 92 had a history of suicide attempt. No association with history of suicide attempt was found in the multiallelic 5-HTTLPR (p = 0.305), however we found significant association with the intron 2 VNTR polymorphism (p = 0.018). When we performed a haplotype analysis, we found association between suicide attempt and haplotype distribution (p = 0.031). These findings suggest that the intron 2 VNTR polymorphism in serotonin transporter gene may influence suicidal behaviour in schizophrenia.

Further evidence of MAO-A gene variants associated with bipolar disorder†

Several lines of evidence suggest that suicidal behavior is associated with altered noradrenergic neurotransmission. Noradrenaline (NA) is catabolized by monoamine oxidase A (MAOA) and cathecol-O-methyl transferase (COMT). We hypothesized that the genes encoding MAOA and COMT might contain genetic variation conferring increased risk for attempted suicide. In order to test this hypothesis, we genotyped the 941T > G and the promoter VNTR polymorphisms in the MAOA gene and the Val 108/158 Met COMT polymorphism in 305 families with at least one member having bipolar disorder (BD). No association with history of suicide attempt was found either in the MAOA polymorphisms (VNTR:LRS = 1.90, d.f. = 1, p = 0.16; 941T > G:LRS = 1.39, d.f. = 1, p = 0.23), or with the Val 158 Met polymorphism (LRS = 1.61, d.f.=1, p = 0.20). When we performed the haplotype analysis for MAOA gene, we found no association between suicide attempt and haplotype distribution (LRS = 3.07, d.f. = 2, p = 0.21). As both genes are involved in degrading noradreanline, we also tested the hypothesis of epistasis between MAOA polymorphisms and Val158Met, however, no additive effect was found in conferring risk for suicide attempt. These findings suggest that MAOA and COMT genes may not influence suicidal behavior in patients with bipolar disorder.